1. Field of the Invention
The invention relates to a method and a liquid preparation for removing residues of auxiliary sawing materials from thin wafers which are obtained by sawing up rod-shaped workpieces, in particular, crystalline rods.
2. Description of the Prior Art
It is known to saw rod-shaped workpieces, especially crystalline rods, composed, for instance, of oxidic materials, such as glass, quartz, gallium gadolinium garnet, sapphire, spinel or composed of semiconductor material such as silicon, germanium, gallium arsenide or indium phosphide into thin wafers. In this connection, the satisfactory separation of the wafers from the workpiece is often assisted by auxiliary sawing materials, for instance, as taught by German Auslegeschrift No. 106 628 (U.S. Pat. No. 3,078,549), by encasing the workpiece in a synthetic-resin sheath composed of epoxy resin. According to the German Offenlegungsschrift No. 3,010,866, separation can also be assisted by cementing several rods together by means of synthetic resin to form a bundle of rods, or, according to German Offenlegungsschrift No. 3,216,200 (U.S. Pat. No. 4,513,544), by cementing the workpiece onto a cutting strip with suitable adhesives, the cutting strip being composed, for example, of graphite or ceramic material, and holding the wafers separated in a multiple internal-hole sawing method. Similar cutting strips are also used in internal-hole sawing with single-wheel systems, especially if the wafers or groups of wafers have to be completely separated in the sawing operation and removed by means of removal devices.
Before further processing of the wafers, such as lapping or polishing, the residues of such auxiliary sawing materials have to be removed. For this purpose, in the prior art discussed above, the wafers are introduced into a trichloroethylene or acetone bath in which the surrounding ring of synthetic resin begins to swell and detach itself. In a similar manner, the residues of the cutting strips which are, as a rule, secured by means of epoxy resin adhesives to the wafers, usually are removed by introduction into a trichloroethylene bath.
It has long been known that many problems are connected with the use of organic solvents such as trichloroethylene or acetone. In this connection, an important aspect of the process is the health risks to the operating personnel which can stem from such use of solvents. These risks require that usually expensive safety precautions be taken and exhaust systems utilized, especially as the baths are operated, as a rule, at elevated temperatures in the vicinity of the boiling point in order to achieve a rapid removal. Moreover, the disposal of such solvents is difficult. Used trichloroethylene is, for instance, not biodegradable and, therefore, has to be disposed of by combustion, for example. In many cases, the fire hazard and the low flashpoint of some organic solvents must also be borne in mind.